Federal and State legislation require control of vehicle exhaust emissions. Oxides of Nitrogen (NOx) are among the exhaust gas emissions that must be controlled. Formation of undesirable NOx gas will occur when there is a high combustion temperature inside of the engine. In an effort to remove or reduce combustion temperatures and NOx emissions, exhaust gas recirculation (EGR) valve systems have been developed. EGR valves function by recirculating a portion of the exhaust gas back to the intake manifold where it will be combined with incoming outside air. The mixing of the exhaust gas and the outside air will displace oxygen in the air intake system. When the mixture is compressed and ignited in the cylinder, the result is a lower combustion temperature (due to the lower levels of oxygen) and a reduction in NOx.
The required EGR valve flow rate is dependent upon several factors that include the displacement of the engine and the engine load condition.
Conventional EGR valves may be actuated by pneumatic or electrical means. Pneumatically actuated valves depend upon the availability of pressure or vacuum on the vehicle and this may be an undesirable requirement. Pneumatic valves also require a means of electrically controlling the pneumatic source to allow overall electrical control of the system. An electric vacuum or pressure regulator is used to provide this control.
Operating force and stroke are factors used in the selection criteria for the type of actuator used for EGR valves. Higher flow rates require larger valves with greater area and corresponding larger strokes and higher operating forces. Lower pressure differential between the exhaust and intake manifold will require larger valves to achieve the desired flow rate. Additionally, contamination in the exhaust gas can accumulate on the valve components and cause them to stick if sufficient operating force is not available. Therefore, it is desirable to provide an EGR valve that has a high operating force, longer operating stroke, and high flow. Another desirable feature is to provide an EGR valve that has a self-cleaning action to prevent the accumulation of contaminants on the operative surface of the valve.